Regulation of gene expression in eukaryotic cells is largely controlled at the level of transcription. This control is mediated by interactions of transacting factors and cis-regulatory sequences. To gain some insights into the mechanisms of trans- activation, we have undertaken studies to examine the ability of two viral early gene products, T antigen of SV40 and E1A protein of adenovirus, to trans-activate human globin gene promoters. Since T antigen and E1A possess both similar and distinct properties in gene regulation, we thought it is important to know the relationship between the two viral proteins in trans-activation of gene expression. This may help us to understand the trans- activation mechanisms of polymerase II transcription in eukaryotic cells. During the past year, we have compared the trans-activation effect of T antigen and E1A by co-transfecting a testing plasmid p-epsilon-GLCAT with either pRSV-T (plasmid expressing the SV40 T antigen) or pE1A (plasmid expressing the E1A protein of adenovirus) into CV-1 cells and COS-1 cells. By transient assay, we found that while both T antigen and E1A trans-activation. We also demonstrated that T antigen can produce additional stimulatory effect on p-epsilon-GLCAT-SV (enhancer+) in CV-1 cells, but E1A has no any effect on this plasmid. Furthermore, whereas introduction of pRSV-T into COS- 1 cells had no effect on p-epsilon-GLCAT expression, the presence of pE1A produced great increase in CAT activity, compared with transfection carried out with p-epsilon-GLCAT alone. Our results, therefore, suggest that T antigen and E1A trans-activate the epsilon-globin promoter by using different mechanisms, probably mediated by different cellular transcription factors.